<!DOCTYPE html>
<html lang="en">

<head>
  <meta charset="UTF-8" />
  <meta http-equiv="X-UA-Compatible" content="IE=edge" />
  <meta name="viewport" content="width=device-width, initial-scale=1.0" />
  <link rel="stylesheet" href="./styles/index.css" />
  <title>Document</title>
</head>

<body>
  <div id="app" class="score-case">
    <div class="table">
      <table>
        <thead>
          <tr>
            <th>编号</th>
            <th>科目</th>
            <th>成绩</th>
            <th>操作</th>
          </tr>
        </thead>
        <tbody v-if="list.length>0">
          <tr v-for="(item,index) in list">
            <td>{{index+1}}</td>
            <td>{{item.subject}}</td>
            <td :class="{red:item.score<60}">{{item.score}}</td>
            <td><a href="#" @click.prevent="del(item.id)">删除</a></td>
          </tr>
        </tbody>
        <tbody v-else>
          <tr>
            <td colspan="5">
              <span class="none">暂无数据</span>
            </td>
          </tr>
        </tbody>

        <tfoot>
          <tr>
            <td colspan="5">
              <span>总分：{{total}}</span>
              <span style="margin-left: 50px">平均分：{{averageScore}}</span>
            </td>
          </tr>
        </tfoot>
      </table>
    </div>
    <div class="form">
      <div class="form-item">
        <div class="label">科目：</div>
        <div class="input">
          <input v-model.trim="subject" type="text" placeholder="请输入科目" />
        </div>
      </div>
      <!-- 
                    type="number"     数字输入框
                    v-model.number    双向绑定数值类型（类型错误，计算结果就错误）
                  -->
      <div class="form-item">
        <div class="label">分数：</div>
        <div class="input">
          <input v-model.number="score" type="number" placeholder="请输入分数" />
        </div>
      </div>
      <div class="form-item">
        <div class="label"></div>
        <div class="input">
          <button class="submit" @click="add">添加</button>
        </div>
      </div>
    </div>
  </div>
  <script src="https://cdn.jsdelivr.net/npm/vue@2/dist/vue.js"></script>

  <script>
    const app = new Vue({
      el: '#app',
      data: {
        list: [
          { id: 1, subject: '语文', score: 20 },
          { id: 7, subject: '数学', score: 99 },
          { id: 12, subject: '英语', score: 70 },
        ],
        subject: '',
        score: ''
      },
      methods: {
        add() {
          if (this.subject === '' || this.score == '') {
            alert('请输入科目和分数')
            return
          }
          this.list.unshift({
            id: +new Date(),
            subject: this.subject,
            score: this.score
          })
          this.subject = ''
          this.score = ''
        },
        del(id) {
          this.list = this.list.filter((item) => item.id !== id)
        }
      },
      computed: {
        //总分
        total() {
          const res = this.list.reduce((sum, item) => sum + item.score, 0)
          return res
        },
        //平均分
        averageScore() {
          if (this.list.length === 0) {
            return 0
          }
          const res = this.total / this.list.length
          return res.toFixed(2)
        }
      }
    })
  </script>
</body>

</html>